Preheat the oven to 350°F (175°C) and grease a 9x13 inch baking pan with cooking spray or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Add in the eggs and vanilla extract, mixing well.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Gradually add the dry ingredients to the wet ingredients, stirring until just combined. If using pecans, fold them into the batter.
In a small bowl, mix together 1/4 cup of brown sugar and 1 tablespoon of cinnamon.
Pour half of the blondie batter into the prepared baking pan and smooth it down evenly. Sprinkle half of the cinnamon mixture over the batter. Add the remaining blondie batter on top and sprinkle with the remaining cinnamon mixture, creating a swirl pattern with a knife or toothpick.
Bake in the preheated oven for 25-30 minutes, or until the edges are golden and a toothpick inserted into the center comes out mostly clean (a few crumbs are okay).
While the blondies are baking, in a medium bowl, combine the softened cream cheese, powdered sugar, milk, and vanilla extract. Whisk until smooth and creamy.
Once the blondies are done baking, let them cool in the pan for about 15-20 minutes. Drizzle the cream cheese glaze over the cooled blondies.
Once the glaze has set slightly, cut the blondies into squares and serve.
Notes
Serve the blondies on a platter with a sprinkle of extra cinnamon and a few chopped pecans on top for an added crunch.